Silicon carbide has been drawing attention as a suitable material of a semiconductor device for attaining a high breakdown voltage and a high current capacity. For example, when manufacturing a bipolar power device with a silicon carbide material, a silicon carbide film is formed on a bulk silicon carbide substrate of a hexagonal system by epitaxial growth, and a pn junction region is formed in the silicon carbide film.
There exists a dislocation referred to as a basal plane dislocation (BPD) in the silicon carbide substrate, and this BPD may be propagated or extended into the silicon carbide film formed by epitaxial growth. A device having the BPD therein is known to have an increased on-resistance when supplied with electricity. The mechanism is considered to: easily disintegrate the BPD into partial dislocations with supplied electricity; and form a high-resistance layer by a stacking fault on a plane between the disintegrated partial dislocations.
On the other hand, step-flow growth of the silicon carbide film is important in order to obtain a smooth surface on an epitaxially grown film. The silicon carbide substrate used for realizing satisfactory step-flow growth is usually off-cut by few degrees from a (0001) plane (a basal plane).
When the silicon carbide substrate with an off-cut angle of 4 degrees is used, the proportion of the BPD in the substrate directly propagated into the epitaxially grown film is considered to decrease remarkably compared with the case where the substrate with the off-cut angle of 8 degrees is used. There is also a reported case where only 3% of the BPD is propagated.
Even with this proportion, the surface of the epitaxial film would have the BPD density of 30 cm−2 when the BPD density in the bulk silicon carbide substrate is approximately 1000 cm−2. Thus, this would be a problem in terms of the manufacturing yield when a power device of a large area is to be formed for attaining high capacity.